2. Selection Tools

Figure 14.8. The Selection tools

2.1. Common Features

Selection tools are designed to select regions from the active layer so
you can work on them without affecting the unselected areas. Each tool has
its own individual properties, but the selection tools also share a number
of options and features in common. These common features are described
here; the variations are explained in the following sections for each tool
specifically. If you need help with what a “selection”
is in GIMP, and how it works, see
Selection.

In some ways the Path tool can also be thought of as a selection tool: any
closed path can be converted into a selection. It also can do a great deal
more, though, and does not share the same set of options with the other
selection tools.

2.1.1. Key modifiers (Defaults)

The behavior of selection tools is modified if you hold down the
Ctrl, Shift, and/or
Alt keys while you use them.

Note

Advanced users find the modifier keys very valuable, but novice users
often find them confusing. Fortunately, it is possible for most
purposes to use the Mode buttons (described below) instead of modifier
keys.

Ctrl

When creating a selection, holding down the
Ctrl key can have two different actions
according to the way you use it:

Holding down the key while drawing
the selection toggles the “Expand from center”
option.

If you hold down the Ctrl key
before drawing a selection, this new
selection switches to the Subtract mode. So, this new
selection will be subtracted from an existing one as soon as
you release the click, as far as they have common pixels.

Alt

Holding Alt will allow movement of the
current selection (only its frame, not its content). If the
whole image is moved instead of the selection only, try
Shift+Alt.
Note that the Alt key is sometimes intercepted by
the windowing system (meaning that GIMP never knows that it was
pressed), so this may not work for everybody.

Shift

When creating a selection, holding down the
Shift key can have two different actions
according to the way you use it:

If you hold down the key before
clicking to start the selection, this
selection will be in Addition
mode as long as you press the key.

If you hold down the Shift key
after clicking to start the selection,
the effect will depend on the tool you are using: for
example, the selection will be a square with the
Rectangle Select tool.

Ctrl+Shift

Using
Ctrl+Shift
together can do a variety of things, depending on which tool is
used. Common to all selection tools is that the selection mode
will be switched to intersection, so that after the operation is
finished, the selection will consist of the intersection of the
region traced out with the pre-existing selection. It is an
exercise for the reader to play with the various combinations
available when performing selections while holding
Ctrl+Shift
and releasing either both or either prior to releasing the mouse
Left Button.

Pressing the Space bar while using a selection
tool transforms this tool into the Navigation cross as long as
you press the bar, allowing you to pan around the image instead
of using the scroll-bars when your image is bigger than the
canvas. This is the default option: in Preferences/Image Windows,
you can toggle the Space bar to the Move tool.

2.1.2. Options

Here we describe the tool options that apply to all selection tools:
options that apply only to some tools, or that affect each tool
differently, are described in the sections devoted to the individual
tools. The current settings for these options can be seen in the Tool
Options dialog, which you should always have visible when you are using
tools. To make
the interface consistent, the same options are presented for all
selection tools, even though some of them don't have any effect for some
of the tools.

Figure 14.9. Common options of selection tools

Mode

This determines the way that the selection you create is combined
with any pre-existing selection. Note that the functions performed
by these buttons can be duplicated using modifier keys, as
described above. For the most part, advanced users use the
modifier keys; novice users find the mode buttons easier.

Replace mode will cause any existing selection to be
destroyed or replaced when the new selection is created.

Add mode will cause the new selection to be added to any
existing selection regions.

Subtract mode will remove the new selection area from any
existing selection regions.

Intersection mode will make a new selection from the area
where the existing selection region and the new selection
region overlap.

Antialiasing

This option only affects some selection tools: it causes
the boundary of the selection to be drawn more smoothly.

Feather Edges

This options allows the boundary of the selection to be blurred,
so that points near the boundary are only partially selected. For
further information regarding feathering, see the glossary entry
Feathering.